In some imaging diagnostic methods, an image of a medical object illuminated with white light and an image of the medical object are acquired in fluorescent light either simultaneously or sequentially. Such methods include photodynamic diagnosis (PDD) and fluorescent endoscopy with indocyanine green (ICG). Two video cameras are customarily used for this process. A first video camera acquires the image resulting from the illumination of the medical object with white light in the visible spectral range, and a second video camera acquires the fluorescent light. Both video cameras can be coupled, for instance by a dichroic mirror, with a single endoscope or a single lens in order to acquire both images from the same perspective.
The use of two video cameras doubles the equipment outlay. In particular, two frame grabbers or video grabbers or image-grabbing switches are necessary for digitizing the video signals of both video cameras. With the computing capacities of computers employed in medical technology today, two separate systems are required for real time processing of the two resulting video streams. The data volume that is to be stored is also doubled and accordingly makes demands on data rates and storage capacities.
If, however, a single video camera system is used for acquiring the image in white light as well as the image in fluorescent light, then the two images can be acquired only in alternation. On switching between the two modes, it is at least necessary to replace observation filters. For instance, in observing the fluorescent light, as a rule one filter is necessary, which blocks the remitted portions of the light used to excite the fluorescence (hereafter referred to as excitation light). Even in cases where a non-simultaneous alternating acquisition of an image and of an image in fluorescent light is acceptable, the requirement to replace the observation filter poses an insuperable technological obstacle. For instance, it is not yet possible to integrate a device for replacing the observation filter on the distal end of a video endoscope.